[libc-commits] [libc] [libc] Implement execvp in unistd (PR #232427)

[Pavel Labath via libc-commits]

================
@@ -0,0 +1,162 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Linux implementation of execvp.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/execvp.h"
+
+#include "hdr/errno_macros.h"
+#include "hdr/types/size_t.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/CPP/stringstream.h"
+#include "src/__support/OSUtil/linux/syscall_wrappers/execve.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+#include "src/unistd/environ.h"
+
+#include <linux/limits.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace {
+
+LIBC_INLINE const char *get_path() {
+  if (LIBC_NAMESPACE::environ == nullptr)
+    return nullptr;
+
+  for (char **env = LIBC_NAMESPACE::environ; *env != nullptr; ++env) {
+    cpp::string_view entry(*env);
+    if (entry.starts_with("PATH="))
+      return *env + 5;
+  }
+  return nullptr;
+}
+
+LIBC_INLINE int execve_with_fallback(const char *path, char *const argv[],
+                                     char *const envp[]) {
+  auto ret = linux_syscalls::execve(path, argv, envp);
+  if (!ret && ret.error() == ENOEXEC) {
+    size_t argc = 0;
+    while (argv[argc] != nullptr)
+      ++argc;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wvla"
+#if __has_warning("-Wvla-cxx-extension")
+#pragma GCC diagnostic ignored "-Wvla-cxx-extension"
+#endif
+    char *new_argv[argc + 2];
+#pragma GCC diagnostic pop
+    new_argv[0] = const_cast<char *>("sh");
+    new_argv[1] = const_cast<char *>(path);
+    for (size_t i = 1; i <= argc; ++i)
+      new_argv[i + 1] = argv[i];
+
+    ret = linux_syscalls::execve("/bin/sh", new_argv, envp);
+  }
+  if (!ret) {
+    libc_errno = ret.error();
+    return -1;
+  }
+  return *ret;
+}
+
+} // namespace
+
+LLVM_LIBC_FUNCTION(int, execvp, (const char *file, char *const argv[])) {
+  LIBC_CRASH_ON_NULLPTR(file);
+
+  if (file[0] == '\0') {
+    libc_errno = ENOENT;
+    return -1;
+  }
+
+  char *const *envp = const_cast<char *const *>(LIBC_NAMESPACE::environ);
+
+  cpp::string_view file_view(file);
+  if (file_view.contains('/'))
+    return execve_with_fallback(file, argv, envp);
+
+  const char *path = get_path();
+  // POSIX standard default path if PATH is not set.
+  if (path == nullptr)
+    path = ":/bin:/usr/bin";
+
+  cpp::string_view path_view(path);
+  bool seen_eacces = false;
+
+  size_t start = 0;
+  while (start <= path_view.size()) {
+    size_t end = path_view.find_first_of(':', start);
+    if (end == cpp::string_view::npos)
+      end = path_view.size();
+
+    cpp::string_view dir = path_view.substr(start, end - start);
+    start = end + 1;
+
+    char path_buf[PATH_MAX];
+    cpp::StringStream ss(path_buf);
+
+    if (dir.empty()) {
+      ss << file << cpp::StringStream::ENDS;
+    } else {
+      ss << dir;
+      if (!dir.ends_with('/'))
+        ss << '/';
+      ss << file << cpp::StringStream::ENDS;
+    }
+
+    if (ss.overflow())
+      continue;
+
+    auto ret = linux_syscalls::execve(path_buf, argv, envp);
+    if (!ret && ret.error() == ENOEXEC) {
+      size_t argc = 0;
+      while (argv[argc] != nullptr)
+        ++argc;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wvla"
+#if __has_warning("-Wvla-cxx-extension")
+#pragma GCC diagnostic ignored "-Wvla-cxx-extension"
+#endif
+      char *new_argv[argc + 2];
+#pragma GCC diagnostic pop
----------------
labath wrote:

Given how hairy this is, we should figure out how to have only one copy of it (merge with execve_with_fallback somehow).

https://github.com/llvm/llvm-project/pull/232427